1. Field of the Invention
This invention relates to a cargo handling pump for transferring the liquid contained in a tank of a vessel or the like.
2. Description of the Related Art
FIG. 6 is a longitudinal sectional view showing a conventional cargo handling pump for transferring a liquid cargo loaded in a vessel tank T.
This cargo handling pump A includes an electric motor 1 disposed above the tank T, a pump 2 disposed at the bottom of the tank T, and a plurality of intermediate shafts 3 which connect the electric motor 1 and the pump 2.
The electric motor 1 is mounted on a motor mount 4 which is detachably fitted on the top surface of the tank T. Couplings 5 and intermediate shafts 3 are alternately connected to the output shaft 1a of the electric motor 1. Protective pipes 6 and bearings 7 are alternately fitted to the underside of the motor mount 4. A centrifugal pump 2 has an end surface thereof fixed to the lowermost protective pipe 6.
The first intermediate shaft 3, the one connected to the output shaft 1a, is supported by a bearing 8 provided in the motor mount 4, while the other intermediate shafts 3 are supported by bearings 7. The lowermost intermediate shaft 3 is connected to the rotary shaft 9 of the centrifugal pump 2, and a discharge pipe 10 connected to the centrifugal pump 2 extends through the top surface of the tank T and opens to the outside. The bearings 7 are arranged such that the intermediate shafts 3 are aligned with each other in a straight line.
If the electric motor 1, after fitting of the thus constructed cargo handling pump A to the tank T, is rotated, an impeller 11 fixed around the rotary shaft 9 is rotated to suck in ambient liquid from the suction side 12 of the centrifugal pump 2 and transfer same via the discharge pipe 10 to the outside of the tank T.
In this case, however, since the tank T has a large size, the entire length of the intermediate shafts 3 between the electric motor 1 and the centrifugal pump 2 is prolonged, thereby requiring an increased number of bearings 7 for supporting the intermediate shafts 3. Thus, a problem arises that the cargo handling pump A requires a large number of parts and its overall weight is increased. Further, due to the structure in which each intermediate shaft 3 is enclosed in the protective pipe 6, it is difficult to perform fine adjustment for centering and aligning the intermediate shafts 3.
Consequently, in case the intermediate shafts 3 are not co-axial, unwanted vibrations are apt to be caused, leading to damage to bearings 7 and to possible trouble during operation of the cargo handling pump. Under these circumstances, a cargo handling pump A1 of the hydraulically driven type as shown below is conventionally used.
The cargo handling pump A1, as shown in its longitudinal sectional view in FIG. 7, comprises a flange 13 fitted to the top surface of the tank T, a protective pipe 14 which is at the upper end fixed to the flange 13 and at the lower end connected with a motor cover 15 in a watertight manner, and a centrifugal pump 2 fixed at the upper end to the motor cover 15. An air chamber 16 is formed inside the protective pipe 14 and the motor cover 15, which air chamber is sealed against the liquid in the tank T. A hydraulic motor 17 is mounted on the upper end surface of the centrifugal pump 2 inside the motor cover 15 so that the rotary shaft 9 of the latter is connected to the output shaft of the hydraulic motor 17.
On the flange 13 is fixed a hydraulic head 18 where hydraulic pipeways are collected. An oil pipe extending from a hydraulic unit (not shown) located outside the tank T and functioning as a hydraulic source is connected to the hydraulic head 18, which hydraulic head is connected through a hydraulic pipe 19 to the hydraulic motor 17.
A branch pipe 20 extends from the hydraulic motor 17 to a bearing 21 for the rotary shaft 9 and to a shaft seal packing 22. The oil having been used to lubricate the bearing 21 is fed through an oil return pipe 23 to the hydraulic head 18. The oil having leaked from the shaft seal packing 22 is contained in a drain receiver 24 provided in the centrifugal pump 2. Air pressure from a pressure source (not shown) located outside is supplied through the protective pipe 14 to the air chamber 16, and from there further to the drain receiver 24 to take the oil in the drain receiver 24 along therewith through an air return pipe 25 to the outside of the tank T.
If hydraulic pressure is supplied from the hydraulic unit through the hydraulic head 18 to the hydraulic motor 17, the hydraulic motor 17 and thus the rotary shaft 9 are rotated to suck in the liquid from the suction side 12 of the centrifugal pump 2 and discharge same through a discharge pipe 10 to the outside of the tank T.
The cargo handling pump A1 as described above is advantageous in that, since no such intermediate shafts 3 as shown in FIG. 6 are used, no vibrations are caused, and that damage to such bearings as 7 and 8 in FIG. 6 can be neglected. The cargo handling pump A1, however, still has drawbacks such as those mentioned below.
(1) The hydraulic unit produces loud noises during its operation which are almost intolerable to inboard residents as well as workers inside and outside the vessel, and has been required to be improved in this respect.
(2) The mechanical efficiency of the hydraulic unit is very low, leading to the loss of lots of energy.
(3) The piping of the high pressure oil and the installation of the hydraulic pressure control equipment are complicated.
(4) The hydraulic motor has an upper limit in the number of revolutions, resulting in the discharge lift of the cargo handling pump limited. For a greater lift a costly two-stage impeller structure must be provided.